1. Field of the Invention
The present invention relates to a USB peripheral apparatus, and more particularly, to a USB peripheral apparatus capable of reducing transmission power and a transmission power reduction method thereof.
2. Description of the Related Art
In the present time, as a USB communication scheme is extensively used in a portable mobile device and the like, a circuit used for USB communication has a large influence on power consumption of a portable apparatus.
Between a host and a device in a USB 2.0 interface, the host is a PC (Personal Computer) and the device is various types of peripheral devices including portable devices such as a memory stick, a cellular phone, a smart phone, or an iPad.
When transmission power of the circuit used for the USB communication is reduced, the use time of the portable apparatus including a battery with limited power increases.
In a USB peripheral apparatus of a USB 2.0 standard, a part using the largest power is a high speed driving circuit.
In the USB 2.0 standard, when the high speed driving circuit transmits data to an external device connected to the USB peripheral apparatus, it is necessary to maintain constant output voltage swing of 400 mV. The voltage swing value is decided by a termination resistance value of a reception circuit, a termination resistance value of a transmission circuit, and a supply current of the high speed driving circuit.
With the recommendation of the USB 2.0 standard, since the termination resistance values of a transmission termination and a reception termination are set to 45Ω, the current of the high speed driving circuit is about 18 mA in order to maintain the output voltage swing of 400 mV.
Since the current of the high speed driving circuit occupies about 40% of the total current used in the USB peripheral apparatus, when the amount of the current of the high speed driving circuit is reduced, the total power consumption of the USB peripheral apparatus is significantly reduced.